netfilter: nfnetlink_queue: drop bogus WARN_ON

Happens when rules get flushed/deleted while packet is out, so remove
this WARN_ON.

This WARN exists in one form or another since v4.14, no need to backport
this to older releases, hence use a more recent fixes tag.

Fixes: 3f801968

 ("netfilter: move nf_reinject into nfnetlink_queue modules")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202407081453.11ac0f63-lkp@intel.com
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>